docs(divergences): narrow the array-map entry to construction past eight

[mparrett]

Why

docs/KNOWN_DIVERGENCES.md still says array-map is routed through the unordered persistent map and points at #763 for scoping. #764 resolved #763 on 2026-09-07 without touching the ledger, and the ledger's own maintenance rule asks for temporary entries to track their resolution. The entry is not gone, though: #764 orders up to eight entries and promotes on the ninth assoc, but (array-map ...) with more than eight pairs is built through the same transient and promotes during construction, so it traverses in hash order where Clojure keeps a directly constructed array map ordered at any size.

What changed

• The "Temporary array-map mismatch" entry now records what feat(vm): insertion-ordered small maps matching Clojure array-map semantics #764 fixed, the residual with a transcript from main at a6763e77, the intended contract, and array-map constructed with more than eight pairs promotes to hash order #827, which tracks the fix.
• The decision paragraph and the portable-code guidance say array-map gives insertion order for up to eight entries, instead of "after the mismatch is resolved".
• last-verified bumped. No other entry changed; both char validation defects still reproduce on the same binary.

Verification

(keys (array-map :i 1 :h 2 :g 3 :f 4 :e 5 :d 6 :c 7 :b 8 :a 9))
;; a6763e77: (:b :g :e :f :a :c :h :d :i)
(keys (array-map :h 1 :g 2 :f 3 :e 4 :d 5 :c 6 :b 7 :a 8))
;; a6763e77: (:h :g :f :e :d :c :b :a)
(int (char 55296))                  ;; 55296, still accepted
(int (char 18446744073709551681N))  ;; 65, still truncated

vm.NewArrayMap in pkg/vm/persistent_map.go builds on a transient, which is where the ninth-entry promotion lives. scripts/docs_frontmatter_hook.py --check passes.

[nooga]

@mparrett Content checks out — I verified the array-map construction-past-eight framing against #764 (merged) and the open #827 tracking issue, and the code in NewArrayMap/NewTransientMap matches what this entry now claims. CI green, no open threads. Green light.

Just sequence this after #825 — both currently touch docs/KNOWN_DIVERGENCES.md/its renamed successor, so rebase onto #825 once that's merged rather than merging in parallel.